Sexual dimorphism in subterranean amphipod crustaceans covaries with subterranean habitat type.

Sexual dimorphism can evolve in response to sex-specific selection pressures that vary across habitats. We studied sexual differences in subterranean amphipods Niphargus living in shallow subterranean habitats (close to the surface), cave streams (intermediate), and cave lakes (deepest and most isolated). These three habitats differ because at greater depths there is lower food availability, reduced predation, and weaker seasonality. Additionally, species near the surface have a near-even adult sex ratio (ASR), whereas species from cave lakes have a female-biased ASR. We hypothesized (a) a decrease in sexual dimorphism from shallow subterranean habitats to cave lake species because of weaker sexual selection derived from changes in the ASR and (b) an increase in female body size in cave lakes because of stronger fecundity selection on account of oligotrophy, reduced predation, and weaker seasonality. We measured body size and two sexually dimorphic abdominal appendages for all 31 species and several behaviours related to male competition (activity, risk-taking, exploration) for 12 species. Species with an equal ASR that live close to the surface exhibited sexual dimorphism in all three morphological traits, but not in behaviour. The body size of females increased from the surface to cave lakes, but no such trend was observed in males. In cave lake species, males and females differed neither morphologically nor behaviourally. Our results are consistent with the possibility that sexual and fecundity selection covary across the three habitats, which indirectly and directly, respectively, shape the degree of sexual dimorphism in Niphargus species.

Another new species of Glossocephalus (Crustacea: Amphipoda: Hyperiidea: Oxycephalidae) from the Monterey Bay region, California, USA.

A new species of Glossocephalus, G. aurantium sp. nov., is described based on two female specimens collected from the Monterey Canyon, California, eastern Pacific Ocean. It was found associated with an undescribed lobate ctenophore. Glossocephalus aurantium is readily distinguished from its congeners by the large crescent-shaped bulbous eye fields relative to the size of the head capsule. The pereopod morphology is most similar to G. rebecae, recently described from the same general region by Zeidler and Browne (2015), but that species is readily distinguished by it's relatively narrow crescent-shaped eye fields. Apart from it's prominent bulbous eye structures, G. aurantium is distinguished from G. milneedwardsi by the morphology of the gnathopods (not spoon-shaped). In addition, pereopods 5 and 6 are slender (not paddle-like) and the head capsule is relatively larger with a sharp rostrum (not rounded).

South America stygobiont crustaceans: a new species of Hyalellidae (Amphipoda) and new reports of Stygocarididae (Anaspidacea) and Protojaniridae (Isopoda) from Calingasta Valley, Pre-Andean region, San Juan, Argentina.

We describe one new eyeless Hyalella species, H. cuyana n. sp., from the hyporheic zone of Calingasta River, San Juan Province, Argentina. Hyalella cuyana n. sp. differs morphologically from its stygobiont congeners by characters of antennae (both antennae subequal in size; aesthetascs elongated); coxal plate 4 (posteriorly without excavation); epimeral plates 1-3 (rounded posterodistally); male gnathopod 2 propodus (almond-shaped, ovate, palm slope strongly oblique); and pleopods (inner ramus reduced to 2-3 articles). We provide a detailed morphological comparison between stygobiont and stygophile Hyalella species. We comment on the sympatry and new report of stygobiont Malacostraca species Parastygocaris andina and Cuyojanira sp. Severe environmental changes and significant decline of habitat quality recorded along the Calingasta River increase the risk of extinction for this vulnerable and endemic fauna. We recommend that the new Hyalella species should be listed as Critically Endangered (CR) in the IUCN categorization according to criteria B1a as it is only known from the type locality; and criteria B1b iii (continuing decline, observed, inferred in the quality of habitat).

Ontogenetic Expressions of Sexually Dimorphic Traits in the Skeleton Shrimp Caprella scaura (Crustacea: Amphipoda).

In sexual dimorphism, males often exhibit exaggerated characters as weapons or ornaments. Among the numerous amphipod species (Amphipoda, Crustacea) showing sexual dimorphism, caprellids (Caprellidae) are characterized by considerably larger males that possess weapons, although the developmental processes underlying these sex-related differences are largely unknown. Therefore, to clarify the process of sexual differentiation during postembryonic development in caprellids, morphometric analyses of Caprella scaura were conducted. Principal component analysis using 31 morphometric traits showed drastic allometric changes occurring at two ontogenetic body length (BL) points (i.e., 3.8 and 8.8 mm). In individuals larger than 3 mm, head spines appeared in both sexes, and penises did only in males, allowing the discrimination of juveniles from larvae. Moreover, in larger males (BL > 8.8 mm), traits used in reproductive behavior, i.e., the first antenna, second gnathopod, and first to fifth pereonites, were extremely exaggerated. Observations of pre-copulatory behavior along with morphological assays revealed that sexually mature males could be identified by the size ratio between the triangular projection and palmar spine on the propodus of the second gnathopod. In contrast, female maturation could be determined by the marginal setae of oostegites forming a brood pouch. The body size distribution of sexually mature females was concentrated within a narrow range of BLs (6-9 mm), whereas that of sexually mature males showed a broader range (BL 9-18 mm), suggesting that, in C. scaura, males continue to molt and grow even after sexual maturation via indeterminate growth, to increase their lifetime reproductive success.

Description of a novel genus with three new species of Phoxocephalidae G. O. Sars, 1891 (Crustacea: Amphipoda) from off northeastern Brazil.

Magnaphoxus ajaja gen. et sp. nov., Ma. simplex gen. et sp. nov. and Ma. longicarpus gen. et sp. nov. are described. The material examined was collected off the states of Cear, Rio Grande do Norte and Bahia during the projects Avaliao da Biota Bentnica e Planctnica na poro offshore das Bacias Potiguar e Cear (BPOT) and Programa de Avaliao do Potencial Sustentvel de Recursos Vivos na Zona Econmica Exclusiva (REVIZEE). Additionally, material from other surveys off Brazilian northeastern coast is included. The samples were collected by rectangular dredges, box corer and Van Veen grabs, ranging from shallow waters to 168 meters in depth. The new genus is morphologically similar to the genera Grandifoxus Barnard, 1979, Metharpinia Schellenberg, 1931, Microphoxus Barnard, 1960 and Rhepoxynius Barnard, 1979. However, it can be recognized by the exclusive constricted and very broad rostrum and bilobated coxa 6, plus the combination of characters such as: lower lip outer plate with apical cusps; right mandible without lacinia mobilis; pereopods 34 carpus posterior margin with one distal robust long seta; propodus strongly armed with robust setae; uropods 12 peduncle dorsolateral margin combed distally; telson with two apical robust setae on each side. All three new species, are fully described, illustrated, and discussed.

A newHyalella species (Crustacea: Amphipoda: Hyalellidae) from South American Highlands (Argentina) with comments on its cuticular ultrastructure.

Hyalella Smith, 1874 includes approximately 92 species present only in the Neotropical and Nearctic regions. Hyalella is a dominant taxon in Central Andean Highland wetlands of Northwestern Argentina. We describe a new Hyalella species from Chorrillos, a cold-hyperfresh Puna peatbog in Salta province. Two other species occur in the Puna biogeographic province, namely H. kochi Gonzlez Watling, 2001 and H. puna Peralta Isa Miranda, 2019. The new species differs from H. puna mainly in having a smooth body surface; propodus of male gnathopod 1 hatchet-shaped, with nine serrate setae on inner margin; uropod 3 peduncle with two strong distal setae; and number and distribution of telson setae; from H. kochi by having the male uropod 1 without modified curved seta on inner ramus; six sternal gills on pereionites II-VII; globose peduncle of uropod 3 with two strong distal setae; long palp of maxilla 1. We also compared its external morphology with that of H. fossamancinii Cavalieri, 1959, another species recorded in the High Andes. We contribute new details on ultrastructural morphology of cuticular extensions (setae; microtrichs; denticles and pores). With this new species, the number of known Hyalella species in Argentina and Falkland Islands (Islas Malvinas) rises to 13.

Physiological and behavioral responses of Orchestia gammarellus (Amphipoda, Talitridae) towards trace elements contamination soil.

Effects of trace elements on the hepatopancreas ultrastructure and on the locomotor activity rhythm were investigated in the amphipod talitrid Orchestia gammarellus collected from Bizerte lagoon banks situated in the north of Tunisia. Animals were exposed to a series of contaminated soil with different concentrations of cadmium and zinc. The locomotor activity rhythm was studied under constant darkness. Histopathological analysis showed that the trace elements, especially the Cd, induced significant changes in the morphology and in the ultrastructural organization of hepatopancreatic cells. The significant alterations obtained were dose dependent. Concerning the behavioral response, results revealed the presence of two components whatever the experimental conditions. In addition, a great inter-individual variability of the locomotor rhythm was observed. Patterns were in majority bimodal for the control individuals and became unimodal and multimodal when exposed under Cd and Zn, respectively. Furthermore, ultradian and circadian periods were determined. The circadian period lengthened after Zn exposure. In addition, the locomotor activity rhythm was more stable for control individuals. However, those exposed to Cd were less active.

A new deep-sea species of Vemana J.L. Barnard, 1964 (Amphipoda, Amphilochidea, Vemanidae) from off southern Gulf of Mexico.

Vemanidae Lowry & Myers, 2017, is an amphipod family restricted to the world's deep waters, with four benthic species inhabiting both bathyal and abyssal zones from the Caribbean Sea, South California, and the Mozambique Channel. During an oceanographic campaign carried out in the southern Gulf of Mexico, a single male specimen of a new species of Vemana J.L. Barnard, 1964 was collected from the deep-sea soft bottom, which is described in detail herein. The new species mainly differs from those four Vemana species by coxa 4 posteroventral corner prolonged forming an acute tooth, basis posterior margin of pereopod 7 with 6 evident teeth, antenna 1 flagellar article 1 lower margin with callynophore, and first urosome segment convex with a diminutive hump. The new species is morphologically closest to Vemana lizata Barnard, 1964, which was collected from the Caribbean Sea at 4077 m depth. Besides, a dichotomous key for the identification of the 5 known Vemana species worldwide is provided.

A subterranean adaptive radiation of amphipods in Europe.

Adaptive radiations are bursts of evolutionary species diversification that have contributed to much of the species diversity on Earth. An exception is modern Europe, where descendants of ancient adaptive radiations went extinct, and extant adaptive radiations are small, recent and narrowly confined. However, not all legacy of old radiations has been lost. Subterranean environments, which are dark and food-deprived, yet buffered from climate change, have preserved ancient lineages. Here we provide evidence of an entirely subterranean adaptive radiation of the amphipod genus Niphargus, counting hundreds of species. Our modelling of lineage diversification and evolution of morphological and ecological traits using a time-calibrated multilocus phylogeny suggests a major adaptive radiation, comprised of multiple subordinate adaptive radiations. Their spatio-temporal origin coincides with the uplift of carbonate massifs in South-Eastern Europe 15 million years ago. Emerging subterranean environments likely provided unoccupied, predator-free space, constituting ecological opportunity, a key trigger of adaptive radiation. This discovery sheds new light on the biodiversity of Europe.

Floresorchestia xueli, a new terrestrial crustacean (Amphipoda, Talitridae) from Yunnan, China.

A new species, Floresorchestia xueli Tong Hou, sp. nov. is described from high altitude habitats of Yunnan, China. The species differs morphologically from its congeners by left mandible lacinia mobilis having four teeth; coxal gills complexly lobed and convoluted; epimeral plates IIIII without slits; telson with one slender facial spine and two terminal spines on each lobe. Analysis of DNA barcode sequences and niche distinctiveness support recognition of the new species.

Three new species of Hyalella (Crustacea: Amphipoda: Hyalellidae) from the Southern Brazilian Coastal Plain.

In this study, three new species of Hyalella (Crustacea: Amphipoda: Hyalellidae) are described based on specimens collected in wetlands located in three freshwater ecoregions (Southeastern Mata Atlântica, Tramandaí-Mampituba and Laguna dos Patos) of the southern Brazilian Coastal Plain (states of Rio Grande do Sul and Santa Catarina). Hyalella minuana n. sp. was recorded in the southernmost region of the state of Rio Grande do Sul. This species is characterized by presenting smooth body surface, epimeral plates not acuminated, nine serrate setae on the inner face of gnathopod 1, and peduncle of uropod 3 with four cuspidate setae with accessory seta and without plumose seta on the margin of the telson. Hyalella lagoana n. sp. was recorded in the northern region of Rio Grande do Sul and southern region of Santa Catarina. This species shows body surface smooth, epimeral plates not acuminated, nine serrate setae on the inner face of gnathopod 1, peduncle of uropod 3 with five cuspidate setae with accessory seta, and telson with six cuspidate setae with accessory seta without plumose seta on the margins. Hyalella sambaqui n. sp. was recorded in the state of Santa Catarina. This species is characterized by presenting smooth body surface, epimeral plates not acuminated, six serrate setae on the inner face of gnathopod 1, peduncle of uropod 3 with three cuspidate setae with accessory seta, and telson with three cuspidate setae with accessory seta and four plumose setae on the margin of the telson. The new records elevates the known diversity of species of Hyalella in the Brazilian territory to 33 species (19 in the southern Brazilian region) and to 83 species in the Americas.

The Caucasian relicts: a new species of the genus Niphargus /(Crustacea: Amphipoda: Niphargidae) from the Gelendzhik-Tuapse area of the Russian southwestern Caucasus.

A new species of the genus Niphargus is described from the Gelendzhik-Tuapse area of the Russian southwestern Caucasus. It belongs to the "puteanus" species group and phylogenetically related to Caucasian N. ciscaucasicus and N. talikadzei, separating from other Caucasian species of the genus by the presence of 2 hooks in retinacules on pleopods, different rami of uropod I both in males and females, and relatively large inner ramus of uropod III. Molecular study has revealed that Niphargus bzhidik sp. nov. and related N. ciscaucasicus are relicts of the Late Miocene speciation, associated with the Messinian crisis (5.96-5.33Mya) separated widespread Paratethys species, which survived in long-term genetic isolation for a long time. The new species is blind and epigean, and probably unable to spread over long distances, but this way of life probably allowed surviving in refugee during the Quaternary period with a colder climate. Analysis of stable isotopes (δ13C/δ15N) revealed that the new species is carnivorous, in contrast to another studied stygobiotic herbivorous Niphargus species (e.g., Niphargus cf. tauricus). The key to the Caucasian and Eastern Asian species of the genus Niphargus, known from the territory of the former USSR, is presented in the article. [http://zoobank.org/urn:lsid:zoobank.org:act:E0019189-2432-4B64-B153-94C43FDD93E3].

More than one way to smell ashore - Evolution of the olfactory pathway in terrestrial malacostracan crustaceans.

Crustaceans provide a fascinating opportunity for studying adaptations to a terrestrial lifestyle because within this group, the conquest of land has occurred at least ten times convergently. The evolutionary transition from water to land demands various morphological and physiological adaptations of tissues and organs including the sensory and nervous system. In this review, we aim to compare the brain architecture between selected terrestrial and closely related marine representatives of the crustacean taxa Amphipoda, Isopoda, Brachyura, and Anomala with an emphasis on the elements of the olfactory pathway including receptor molecules. Our comparison of neuroanatomical structures between terrestrial members and their close aquatic relatives suggests that during the convergent evolution of terrestrial life-styles, the elements of the olfactory pathway were subject to different morphological transformations. In terrestrial anomalans (Coenobitidae), the elements of the primary olfactory pathway (antennules and olfactory lobes) are in general considerably enlarged whereas they are smaller in terrestrial brachyurans compared to their aquatic relatives. Studies on the repertoire of receptor molecules in Coenobitidae do not point to specific terrestrial adaptations but suggest that perireceptor events - processes in the receptor environment before the stimuli bind - may play an important role for aerial olfaction in this group. In terrestrial members of amphipods (Amphipoda: Talitridae) as well as of isopods (Isopoda: Oniscidea), however, the antennules and olfactory sensilla (aesthetascs) are largely reduced and miniaturized. Consequently, their primary olfactory processing centers are suggested to have been lost during the evolution of a life on land. Nevertheless, in terrestrial Peracarida, the (second) antennae as well as their associated tritocerebral processing structures are presumed to compensate for this loss or rather considerable reduction of the (deutocerebral) primary olfactory pathway. We conclude that after the evolutionary transition from water to land, it is not trivial for arthropods to establish aerial olfaction. If we consider insects as an ingroup of Crustacea, then the Coenobitidae and Insecta may be seen as the most successful crustacean representatives in this respect.

Friction reduction mechanism of the cuticle surface in the sandhopper talitrus saltator (Amphipoda, talitridae).

In many cases, strong friction reduction is critical for success of both living organisms and engineering systems. Some arthropods exhibit good antifriction abilities in their specific living environments and have inspired many innovations for solving industry challenges. However, the current literature mainly focused on terrestrial insects, such as beetles, grasshoppers and katydids. The antifriction mechanisms in amphibious arthropods are still unknown, even if their surfaces are optimized for both air and water environments. Herein the tribological properties of the cuticle surface of the sandhopper Talitrus saltator were studied using a universal microtribometer. Further investigations were developed to identify the microstructural, compositional, wettability, and mechanical properties of the sandhopper shell cuticles. It was found that increasing normal force can significantly reduce the coefficient of friction of the shell cuticle, especially for the alive and rewet sandhopper shells. The shell consists of bottle-like nano-caves in its exocuticle, nano-tubes in its mesocuticle, and gauze-like multilayers in its endocuticle. Under physiological conditions, glycoprotein-like fluid fillings exist in both the bottle-like caves and the nano-tubes below and cover on the shell surface. More importantly, a new antifriction mechanism of lubricant-squeezing nano-porous system was established for the sandhopper shell. This work can deepen our understanding in antifriction surfaces of amphibiotic crustaceans, and provide a potential approach to resolve the friction challenge in micro-machines, especially for the applications under aqueous condition. STATEMENT OF SIGNIFICANCE: Friction regulation is one of the critical mechanisms for animal locomotion in natural environments. However, not much is known about the mechanism of amphibious arthropods to reduce friction between their body and diverse environments, particularly achieving adaption under both air and aqueous conditions. We quantitatively study the microstructural, compositional and mechanical properties of the sandhopper (Talitrus saltator) shell cuticle and tribological behaviors under different conditions. Our results reveal the nano-porous system with fluid fillings for the sandhopper's shell and demonstrate the potential antifriction mechanism of this amphibious animal. We anticipate this work will inspire some effective antifriction designs for micro-machines, especially for their applications in complex environment like human body.

The induced damage in the hepatopancreas of Orchestia species after exposure to a mixture of Cu/Zn-An ultrastructural study.

The hepatopancreas of crustaceans species has been recognized as an essential target organ to assess trace elements' effects. Due to its dynamic and capability of detoxifying trace metal, this organ often indicates distinct pathological disturbances. In the present work, we intend to evaluate the bioaccumulation of trace metal in three Orchestia species (Orchestia montagui, Orchestia gammarellus, and Orchestia mediterranea) living in symmetry in the banks of Bizerte lagoon (37°13'8″N 09°55'1″E) after their exposure during 14 days to a mixture of copper and zinc, and to highlight the effect of these metals on their hepatopancreas ultrastructure using transmission electron microscopy. At the end of the experiment, results showed that the mortality and the body mass varied according to the used nominal concentrations. Significant alterations were noted in all the treatment groups. The degree of these alterations depends on the used concentration, and they are represented especially by the cells remoteness and the border lyses, the reduction of the nuclear volume, the increase in the cytoplasm density with the presence of trace metal in the nucleus as well as in the vacuole, the disorganization and the destruction of microvilli, the condensation of the majority of cellular organelles and mitochondria swelling. Through this study, Orchestia genus could be an attractive candidate for the biochemical study of trace metal toxicity in Tunisian wetlands.

CO2 leakage simulation: Effects of the decreasing pH to the survival and reproduction of two crustacean species.

The effects of CO2-related acidification on two crustacean populations, the isopod Cyathura carinata and the amphipod Elasmopus rapax, were studied. Three pH levels were tested: artificial seawater without CO2 injection and two levels of reduced pH. Even though RNA:DNA ratio was reduced for both species, no statistical significant differences were found between the control and the treatments. Both species experienced a reduction in survivorship, longevity and the body length of surviving animals; although the impairment observed in E. rapax was more severe than in C. carinata. The long life span isopod and the short life span amphipod experienced a high degree of impairment in the reproduction, likely due to the reallocation of resources from reproduction to body maintenance and increasing survival by postponing the brood production. Regardless of the underlying processes and the energetic pathways, both experienced failure to reproduce, which could lead to the local extinction of these species.

Ecological aspects of natural populations of Hyalella pampeana (Crustacea, Amphipoda, Hyalellidae) from the Natural Reserve Island of Martín García (Río de La Plata, Argentina).

Freshwater amphipods of the genus Hyalella have a great importance in aquatic ecosystems due to their role in matter and energy cycling and its utilization as bioindicators of environmental health. The aim of this work was to analyze relevant population parameters of Hyalellapampeana, such as population density and structure, individual body size, sex ratio, fecundity and recruitment, and to study the possible relation of these parameters to variations in environmental variables. Samples were taken monthly during a one-year period (2006) at three small ponds in the Natural Reserve Island of Martín García, Argentina. The inland aquatic environments showed distinctive physicochemical characteristics, mainly related to pH and conductivity values. Amphipod population density varied among sites and throughout the year, with population peaks during spring, positively correlating with pH values. The operational sex ratio of the total population was almost equal to 1 male: 1 female, displaying seasonal variation. Mean fecundity and mean size of ovigerous females were higher during winter and early spring months than in summer months. The presence of ovigerous females and juveniles in all months indicated that reproduction is continuous during the year for Hyalella, in its natural environment.

The family Phoxocephalopsidae (Crustacea: Amphipoda) from Brazilian coastal waters with description of four new species.

Phoxocephalopsids are fossorial amphipods endemic to the Southern Hemisphere and currently encompass five genera and 15 species, including the four new species herein described. Previous records of the family along the Brazilian coast are limited to Phoxocephalopsis zimmeri Schellenberg, 1931. Based on material from the Crustacean Collection of Museu Nacional/UFRJ four new species of Phoxocephalopsidae areherein described: Phoxocephalopsis ruffoi sp. nov. from Rio de Janeiro, São Paulo, Paraná and Rio Grande do Sul (23o-30oS); Puelche irenae sp. nov. from Espírito Santo and Rio de Janeiro (19o-23oS); Puelche longidactylus sp. nov. from Bahia, Espírito Santo and Rio de Janeiro (12o-23oS) and Puelche mourae sp. nov. found only at Rio de Janeiro. High diversity was recorded from the Campos Basin region, which extends from the north of Rio de Janeiro to south of Espírito Santo (21o-23oS), with the presence of all four phoxocephalid species. A key to Phoxocephalopsidae species from Brazil, including P. orensanzi Barnard and Clark, 1982 is provided.

Discovery of a new genus and species of dogielinotid amphipod (Crustacea: Amphipoda: Dogielinotidae) from the Nipa palm in Thailand, with an updated key to the genera.

During a scientific survey, a new genus of the dogielinotid amphipoda was found in the Nipa palm (Nypa fruticans) in Bang Krachao Urban Oasis, Samut Prakan Province, Thailand. We placed this new genus, Allorchestoides gen. nov., within the family Dogielinotidae. The new taxa can be easily distinguished from the remaining genera by differences in the incisor of the left and right mandibles, apical robust setae of the maxilla 1, and the large coxa and strong obtuse palm in the female gnathopod 1. The type species of Allorchestoides gen. nov., Allorchestoides rosea n. sp., is described here in, with an updated key to the genera of the family Dogielinotidae.

Reassessment of the Groundwater Amphipod Paramoera relicta Synonymizes the Genus Relictomoera with Paramoera (Crustacea: Amphipoda: Pontogeneiidae).

The systematic status of the stygobitic amphipod, Paramoera relicta Uéno, 1971, was revisited based on morphological examination of the paratypes, and molecular phylogenetic analyses using a newly collected specimen from its type locality. The paratypes clearly showed that this species does not possess the "sinusoid" antennal sinus in the head, which was erroneously described in the original description of this species; P. relicta is unquestionably classified within the genus Paramoera Miers, 1875 . Molecular phylogenetic trees obtained with nuclear histone H3 and mitochondrial 16S rRNA demonstrated that P. relicta clearly belongs to the clade consisting of Paramoera species. Since the genus Relictomoera Barnard and Karaman, 1982 was erected according to the "sinusoid" characteristic of its type species P. relicta, this genus is no longer valid, and should be treated as a junior subjective synonym of Paramoera. One of the paratypes of P. relicta is herein designated as a neotype for the species to clarify its taxonomic status and emend the morphological characteristics of this pontogeneiid amphipod.